USB Condensor as a "field-grade" USB mic for lapto

[Haysus]

Did you have any luck? I am considering a the same idea to ballpark the system room to room.Cheap and easy are my favorites when it comes to setup.

[Ron K]

http://www.markertek.com/SearchProduct. ... agesize=20

Inexpensive xlr to uSB with phantom power. add the 50.00 behringer and for 100.00 your in right.

[bgavin]

My concern with phantom power is the minuscule 500mA maximum current from the on-board USB port.

Rolls, among others, makes a very small and portable +48v phantom supply powered by a 120v circuit. These do not have current limitations that will starve a hungry condenser mic or over stress the USB port.

[Ron K]

I wasn't aware of even large diaphragm condensers drawing over 20ma? I thought most only drew about 6ma @ 48V.

Some preamps like in acoustics draw a bit more but I always thought they were under 85ma.?

I was aware of 24 volt phantoms having more current draw but that's due to the lower voltage.

What condensers draw at that high +200ma range? Very curious.

[bgavin]

The Earthworks draw about 10mA, and they are the highest I know about.
The average draw for those I have data is 3.5mA.

My concern is strictly gut level, since the USB circuit is called on to step up 5v to 48v.
500mA at 5v is 2500mW.
52mA at 48v is 2500mW as a lossless transformation.

USB circuits are fragile and not intended to produce any meaningful amount of power.
I've seen several USB burned out on laptops. Cause unknown.
This can be completely avoided by using a powered USB hub.

I have a recording friend in Oklahoma who swears he can hear the difference between USB phantom and 120v transformed phantom. I have no measurement experience here, only anecdotal.

[RayAbbitt]

I wasn't aware of even large diaphragm condensers drawing over 20ma? I thought most only drew about 6ma @ 48V.

Some preamps like in acoustics draw a bit more but I always thought they were under 85ma.?

WELL under 85 ma. Standard (48 volt) phantom power is applied through 2 6800 ohm resistors (one to signal plus, one to signal minus) and the dc return is the shield of the cable. With both sides shorted to ground the maximum current would be 14 ma. (Ohms law, 2 6800 ohm resistors in parallel=3400 ohms. 48V/3400 ohms=14ma)

I was aware of 24 volt phantoms having more current draw but that's due to the lower voltage.

More is relative. If they draw more than 14 ma they won't work with most mixers. Keep in mind that the phantom was originally designed to be a bias voltage, not a power supply.

What condensers draw at that high +200ma range? Very curious.

None (but if they did, they would have their own power supply)

-ray

[Ron K]

Thanx for the reply and clarifications Ray.

Your thoughts on a standard USB ports ability to provide sufficient current for 48V Phantom power.What about with a long mic cable attached say 50 to 100 ft?

[Sydney]

* I haven't tried what your doing Ron,..
But considering a POTS system is 48V and a typical device uses approx 20ma over thousands of feet of 22 - 24 AWG unshielded.
Good shielded mic cable should be fine ( available as large as 18 AWG ) so I wouldn't expect any problems.
http://www.sengpielaudio.com/calculator-cable.htm

[Sydney]

Standard (48 volt) phantom power is applied through 2 6800 ohm resistors

Illustrated here:
http://www.tangible-technology.com/powe ... nnect.html

An example of a mic cable length recommendation rating I found:
A Schoeps mic ( 10V ) is rated for 100 meters using ordinary mic cable and up to 400M with 110 ohm AES-3 cable.

[RayAbbitt]

Thanx for the reply and clarifications Ray.

Your thoughts on a standard USB ports ability to provide sufficient current for 48V Phantom power.What about with a long mic cable attached say 50 to 100 ft?

I've used an M-Audio MobilePre (2channel USB audio interface with mic preamps and phantom power) along with a pair of condensor mics to record to my laptop with no problems. And that was with the mics connected via 100 foot snake with 25 foot mic cables on each end (150 feet total). Worked fine.

-ray